1. Field of the Invention
The invention relates to a gas turbine combustion chamber having an annular combustion space whose walls extend from the combustion chamber inlet to the inlet to the gas turbine, and in which the combustion chamber inlet is equipped with a plurality of burners evenly distributed in the peripheral direction, which burners are fastened to a front plate.
2. Discussion of Background
The so-called "weak premixing combustion" has, in the recent past, become general for the low-pollutant combustion of a gaseous or liquid fuel. In this, the fuel and the combustion air are premixed as evenly as possible and are only then supplied to the flame. If this is carried out with a large excess of air, as is usual in the case of gas turbine installations, relatively low flame temperatures occur and this in turn leads to the desired, low level of formation of nitrogen oxides.
Combustion chambers of the type mentioned at the beginning are known from EP-A1-387 532. In this, the front plate is formed by a single wall on which are arranged premixing burners of the double-cone type.
Modern highly-loaded gas turbines demand increasingly complex and effective cooling methods. In order to achieve low NO.sub.x emission, attempts are made to direct an increasing proportion of the air through the burners themselves. This necessity to reduce the cooling air flows is also, however, due to reasons associated with the increasing hot gas temperature at the inlet of a modern gas turbine. Because the cooling of the other installation parts such as blading, machine shaft, etc. must also meet increasingly stringent requirements and because the hot gas temperatures, which continue to be increased in the interest of a high thermal efficiency, also lead directly to a greatly increased thermal loading on the combustion chamber walls, it is necessary to be very economical with the combustion chamber cooling air. These requirements generally lead to multi-stage cooling techniques, in which the pressure loss coefficient, i.e. the overall pressure drop caused by the cooling divided by a stagnation pressure at the cooling air inlet into the combustion chamber, can be quite high.
Gas turbine combustion chambers with air-cooled flame tubes are likewise known, for example from U.S. Pat. Nos. 4,077,205 or 3,978,662. The flame tube is essentially constructed of wall parts overlapping in the axial direction of the turbine. On their side facing away from the combustion space, each of the wall parts has a plurality of inlet openings distributed over the periphery. These inlet openings are used to introduce air into a distribution space arranged in the flame tube and communicating with the combustion space. In the case of the cooling system in these specifications, the respective flame tube has a lip which extends over the slot through which the cooling air film emerges. This cooling air film is to adhere to the wall of the flame tube, in order to form a cooling barrier layer for the flame tube.
The known gas turbine combustion chambers mentioned above have the disadvantage that the air consumption for cooling purposes is much too high and that, because the cooling air is fed into the flame tube interior downstream of the flame, this air is not available for the actual combustion process. The combustion chamber cannot, in consequence, be operated with the high excess air ratio necessary.
In the case of conventional combustion chambers, the cooling generally plays an extremely important role in the noise damping of the combustion chamber. The reduction in the cooling air mass flow mentioned above, in association with a greatly increased pressure loss coefficient for the overall combustion chamber wall cooling, now leads to an almost complete suppression of the noise damping. This development has led to an increasing vibration level in modern low NO.sub.x combustion chambers.